Ozone, which causes photochemical smog, is produced by a photochemical reaction of HC and NOx contained in exhaust gases from automobiles and factories. Therefore, reducing the amount of HC and NOx emissions from automobiles is an efficient way to suppress the production of ozone and the occurrence of photochemical smog. Also, purifying ozone in the air directly can be one of the ways to prevent the occurrence of photochemical smog. By purifying ozone as a product as well as reducing the amount of emissions of HC and NOx as reactants, the occurrence of photochemical smog can be prevented more effectively. Thus, an automobile including a vehicular air cleaner capable of directly purifying ozone in the air has been put into practical use in some places including California in the United States of America. Such a vehicular air cleaner is called a DOR (Direct Ozone Reduction) system.
For example, Patent Literature 1 discloses a DOR system in which a vehicle component part carries metal oxide such as manganese dioxide. The vehicle component part is arranged at the position where the part is exposed to air, and the manganese dioxide has a function for converting ozone contained in the air into other substances such as oxygen and purifying the ozone. Thus, according to the DOR system disclosed in Patent Literature 1, ozone in air can be directly purified while a vehicle is moving.